The present invention relates generally to a rolling mill and a rolling-mill train and more particularly to a rolling mill and a rolling-mill train to roll workpieces into products such as steel bars, wires, and pipes. The word of xe2x80x9cproductsxe2x80x9d used in this specification means a concept including steel bars, wires, and pipes.
A multi-stage four-roll or three-roll rolling-mill train rolls a workpiece in four or three directions repeatedly, reducing its sectional area gradually, to form it into a desired shape of desired dimensions.
Typical four-roll rolling mills used in the above rolling is shown in FIGS. 9 and 10. In FIG. 9, an input shaft 101 drives four rolls 102, 103, 104, and 105. The input shaft 101 is coupled with one roll 102. Each of the four rolls 102, 103, 104, and 105 has bevel gears (102b, 103b, 104b, or 105b as the case may be) on both its sides. When the input shaft 101 turns the roll 102, the driving power of the input shaft 101 is transmitted to other rolls 103, 104, and 105 through the bevel gears 102b, 103b, 104b, and 105b. 
FIG. 10 shows a four-roll rolling mill which is similar to the rolling mill of FIG. 9 but of which the rolls are slanted by 45xc2x0 relatively to horizontality and verticality. Its input shaft protrudes diagonally upward. Accordingly a reducer to be coupled with the input shaft has to be tall and bulky, occupying a large space and increasing the equipment cost.
To increase the dimensional accuracy of products, it is effective to roll workpieces with a multi-stage rolling-mill train consisting of rolling mills which are arranged in tandem and of which the roll units have phase angles minutely different from one another.
In case of a stretch reducer for pipes in particular, the inner surfaces of pipes tend to become squarish or polygonal. Such tendency can be reduced considerably by adjusting its roll phase angles minutely and pipes with round inner surfaces can be produced.
In case of rolling mills in accordance with the prior art, if the roll phase angle of a rolling mill is changed, its reducer becomes bulky. If a rolling mill is given a housing of which the disposition can be changed to adjust the roll phase angle, its reducer becomes complex.
In view of the foregoing, the object of the present invention is to provide a rolling mill and a rolling-mill train which are compact. Reducers to be coupled with them can be made compact. The inner surfaces of pipes to be rolled with the rolling mill and the rolling-mill train can be prevented from becoming squarish.
According to the first aspect of the present invention, there is provided a rolling mill comprising (i) a roll unit including a plurality of rolls disposed symmetrically around the pathline of the rolling mill and (ii) a driving unit for driving and rotating the rolls. The driving unit has an annular driving bevel gear of a large diameter, an input-shaft mechanism for rotating the driving bevel gear, a plurality of transmission mechanisms disposed at regular intervals along the driving bevel gear and transmitting the rotation of the driving bevel gear to the rolls, and a housing for holding them. The input-shaft mechanism has an input shaft inserted in the housing from its outside and an input bevel gear of a small diameter mounted on the input shaft and engaging with the driving bevel gear. The input-shaft mechanism is disposed between two adjacent transmission mechanisms.
According to the second aspect of the present invention, there is provided the rolling mill of the first aspect, wherein each transmission mechanism comprises (i) a first transmission shaft on which mounted is a transmission bevel gear of a small diameter engaging with the driving bevel gear, (ii) a first cylindrical gear mounted on the first transmission shaft, (iii) a second transmission shaft coupled with a shaft of a roll, and (iv) a second cylindrical gear mounted on the second transmission shaft and engaging with the fist cylindrical gear.
According to the third aspect of the present invention, there is provided the rolling mill of the second aspect, wherein (i) the input shaft of the input-shaft mechanism takes the place of the first transmission shaft of one of the transmission mechanisms and is disposed in parallel with the second transmission shaft and (ii) the first cylindrical gear is mounted on the input shaft and engages with the second cylindrical gear of the second transmission shaft.
According to the fourth aspect of the present invention, there is provided the rolling mill of the third aspect, wherein a first bevel gear takes the place of the first cylindrical gear of the input shaft and a second bevel gear takes the place of the second cylindrical gear of the second transmission shaft.
According to the fifth aspect of the present invention, there is provided a rolling-mill train comprising a plurality of rolling mills of the first aspect. Their input shafts are disposed horizontally and the phase angles of their roll units are different from one another.
According to the sixth aspect of the present invention, there is provided a rolling-mill train comprising a plurality of rolling mills of the fourth aspect. Their input shafts are disposed horizontally and the phase angles of their roll units are different from one another.
According to the seventh aspect of the present invention, there is provided a rolling-mill train comprising the rolling mill of the third aspect with its input shaft disposed horizontally, the rolling-mill train of the fifth aspect, and the rolling-mill train of the sixth aspect all arranged in tandem.
The advantage offered by the first aspect of the present invention is as follows. When the torque of an external driving-power source is transmitted to the driving bevel gear, the driving bevel gear rotates. The rotation is transmitted through a plurality of transmission mechanisms to the rolls. Thus the rolls rotate to roll a workpiece. Because the input-shaft mechanism is disposed between adjacent two transmission mechanisms, the angles between the input-shaft mechanism and the two transmission mechanisms can be set freely so long as they do not interfere with each other. In other words, the phase angle of the roll unit can freely be changed while the input shaft is kept horizontal. Therefore, by arranging a number of rolling mills of this aspect in tandem, a rolling-mill train with roll phase angles minutely different from one another can be made.
The advantages offered by the second aspect of the present invention are as follows. The rotational torque of the driving bevel gear is transmitted to the rolls through the first cylindrical gear of the first transmission shaft and the second cylindrical gear of the second transmission shaft, engaging with each other, of each transmission mechanism; therefore the driving force can be utilized efficiently with a small transmission loss. Besides, because the transmission mechanisms are compact, they are less likely to interfere with the input-shaft mechanism; therefore the phase angle of the transmission mechanisms and hence that of the roll unit can be adjusted in a large range.
The advantage offered by the third aspect of the present invention is as follows. The input shaft takes the place of the first transmission shaft in one of the transmission mechanisms and torque is transmitted from the input shaft to the second transmission shaft through the first and second cylindrical gears engaging with each other. Accordingly the rolls can be disposed horizontally and vertically with the input shaft disposed horizontally and in parallel with the second transmission shaft.
The advantage offered by the fourth aspect of the present invention is as follows. The rotational torque of the input shaft is transmitted to the second transmission shaft through the first and second bevel gears. By changing the diameters of the first and second bevel gears, the angle between the input shaft and the second transmission shaft can be changed freely. Accordingly while the input shaft is kept horizontal, the phase angle of the roll unit can be changed freely. Therefore, by arranging a number of rolling mills of this aspect in tandem, a rolling-mill train with roll phase angles minutely different from one another can be made.
The advantages offered by the fifth aspect of the present invention are as follows. Because the rolling-mill train consists of rolling mills with roll phase angles minutely different from one another, a workpiece can be rolled in many different directions; accordingly high rolling accuracy can be achieved and the inner surfaces of pipes can be prevented from becoming squarish. Because the input shafts of all the rolling mills are disposed horizontally, the coupler portions with reducers are not bulky. Moreover, it is not necessary to provide reducers with a transmission bevel gear; therefore they do not become bulky.
The advantages offered by the sixth aspect of the present invention are as follows. Because the rolling-mill train consists of rolling mills with roll phase angles minutely different from one another, a workpiece can be rolled in many different directions; accordingly high rolling accuracy can be achieved and the inner surfaces of pipes can be prevented from becoming squarish. Because the input shafts of the rolling mills in the train are disposed horizontally whereas their rolls are slanted, the couplers with their reducers are not bulky.
The advantages offered by the seventh aspect of the present invention are as follows. Because a rolling mill with horizontal and vertical rolls and a plurality of rolling mills with roll phase angles minutely different from one another are arranged in tandem, the rolling accuracy is high and the inner surfaces of pipes can be prevented from becoming squarish. In addition, because all the input shafts are horizontal, the couplers with their reducers are not bulky.